Comparison of a batch, fed-batch and continuously operated stirred-tank reactor for the enzymatic synthesis of (R)-mandelonitrile by using a process model

Abstract

The suitability of a batch, fed-batch and continuously operated stirred-tank reactor for the enzymatic production of (R)-mandelonitrile in an aqueous-organic biphasic system was investigated by using a process model. The considered biphasic system is 10–50% (v/v) 100 mM sodium citrate buffer of pH 5.5 dispersed in methyl tert-butyl ether. The constraints were that 750 moles of benzaldehyde per cubic meter should react towards (R)-mandelonitrile with an enantiomeric excess of 99% and a conversion of 98%. A continuously operated stirred-tank reactor could not meet the constraints, but the production in a batch or fed-batch reactor was feasible. The choice for a batch or fed-batch reactor is dependent on the influence of the costs for reactor operation and for the enzyme on the product costs. The choice for operating at a small or large aqueous-phase volume fraction is dependent on the costs and reusability of the enzyme. The volumetric productivity is maximal when operating as batch. The enzymatic productivity and turnover are maximal when operating as fed batch. In the fed-batch mode, the enzymatic productivity increased by 24–37%, the turnover increased by 50–60% and the volumetric productivity decreased by 33–71% as compared to a batch reactor. By enhancement of mass transfer both the volumetric and enzymatic productivity can be increased considerably, while the turnover is only slightly decreased.